The present invention is related to a method for making microemulsions. More particularly, the present invention is related to a method for making microemulsions having an average particle size of 0.05 microns and below.
Microemulsions containing aminofunctional silicone fluids have been found to be useful in hair car compositions, such as hair conditioners. As defined herein, the term "microemulsions" refers to transparent, stable systems consisting of small droplets having an average diameter of 0.05 microns or below. The small size of the droplets makes the microemulsion transparent in appearance. Products containing microemulsions are valued for their stability and small particle size which gives the product increased aesthetic value.
The use of microemulsions in cosmetic compositions is known in the art. Reference is made, for example, to U.S. Pat. Nos. 4,797,272 (Linn et al.) and 4,620,878 (Gee).
U.S. Pat. No. 4,797,272 (Linn et al.) discloses water-in-oil microemulsion compositions having an average droplet size in the range of about 0.001 microns to about 0.2 microns in diameter and containing moisturizers or sunscreens, surfactants, oils (such as cyclic dimethyl polysiloxane compounds), and skin humectants.
U.S. Pat. No. 4,620,878 (Gee) discloses a polyorganosiloxane emulsion containing a polyorganosiloxane containing at least one polar radical, e.g., an amine radical, attached to Si through Si--Ci or Si--O--C bonds or at least one silanol radical and a surfactant which is insoluble in the polyorganosiloxane. The emulsion prepared in Gee has an average particle size of less than 0.14 microns and can be prepared by forming a translucent oil concentrate by mixing the polyorganosiloxane (which can be amino-functional), at least one surfactant, and water, and then forming a polyorganosiloxane emulsion of the oil-in-water type by rapidly dispersing the translucent oil concentrate in water.
It is continually desirable to provide alternative methods for preparing microemulsions of small average particle size.
The present invention is based on the discovery that the average particle size of an amino-functional silicone microemulsion can be reduced to a value in the range of from 0.015 to about 0.05 microns by adding a saturated, lower aliphatic carboxylic acid after the addition of water and surfactant to the amino-functional silicone fluid and further by adding the water in two separate portions wherein the first portion is added slowly to the silicone fluid and surfactant mixture.